This investigation extends a quantitative experimental model designed to analyze biological and physical aspects of repair in canine segmental fibular cortical bone grafts. Studies will be conducted to determine if freeze-dried cortical allografts with relatively short-term immunosuppression with Imuran will mimic similar but fresh autografts rather than fresh allografts. This potential approach for an alternative to fresh autografts is based on the following: (1) Insignificant differences were determined between bilateral fresh and freeze-dried autografts (hence, a viable graft does not necessarily enhance incorporation); (2) Significant differences were found between an autograft and a fresh or freeze-dried allograft (hence, freeze-drying does not protect allografts from rejection); (3) The rejection of fresh allografts was significantly altered with continuous or short-term use of Imuran while normal autogenous graft repair was maintained; and (4) Alternative sources to autogenous bone are often required for reconstructive procedures. The proposed study will be quantitated by continuous tetracycline labelling, microradiography, roentgenograms, and torsional loading to failure.